Another A/C question

[rbev2308]

First off, I have searched all the a/c related stuff and quite a bit of it has helped me so far but have one thing frustrating me. Noticed recently that having a hard time on zone 1 of my Alpine getting the temp below 75 on days with 80+ outside. Zone 2 is easy. I noticed CFM with basic hand test was not really the issue and I checked for crushed returns. I am finding poor HVAC jobs when I pull the ceiling vents and the tape was never done properly so ambient air is filtering into the cool air coming thru. Probably explains the 7-9 degree increase temp coming out compared to zone 2. Upon pulling the first return, I took pics with my cell phone and noticed wiring which is probably near the bottom of the a/c unit on the roof and what appeared to be a hole about half way down. No darn way I could repair that but what is perplexing is I am getting forced cold air coming out the return and cannot pinpoint why or my next course of action I should investigate. Yes the thing is under warranty but I really do not feel like making an appt, dragging the thing in, losing for several weeks to fix something I would probably attempt to do if it were not under warranty. Any ideas on why or how I am losing air and its making its way into the return line? Checking all the other returns now!

[rbev2308]

UPDATE ON THE AC ISSUE:

After pulling every return, every supply vent and re-taping, pulling the shroud to check any damage at the roof top level, here are my results.

Set unit daily to 70 degrees first thing in the morning. We have had days were highs are 79 up to 89. Zone 2 continues to put out mid 40's air and remain at 70 and cycle on and off. Zone 1 continues to put out 53-59 degree air, return temps in the 70's and living room stays 70 till about noon and then within 3 hrs it is 75-76 and remains that way. Tried with all blinds closed, ceiling fan running, ac fan on high. Have noticed slide ceiling temps at 80+ degrees. Great CFM and always over 18 degree + difference in return versus supply so local Dometic rep says no way anything is wrong with unit that it would be either insulation issue or air leak. Even put my remote imaging camera into both returns and several vents and saw nothing alarming. Even sticking handheld thermometer in return notice no variance in temps. Very perplexing as it just seems I am destined to get no better than 75 even on days outside temps at 80 and even 90. Not sure if any other Alpine or similar 5ers are getting same results. I even had my parents check their 2010 Alpine and it has same Dometic setup with heat pump and ac and they are not getting same results. At a loss....any advice other than suck it up!!!! Thanks!

Also..not a sensor issue as the handheld thermometer matches thermostat sensor temp!!!

[cb1000rider]

I don't have any great answers for you, but I've run into the same thing with ducted AC units. You're essentially passing cooled air through roof space with limited to no insulation (after accounting for the space of the duct) and these units always perform worse than non-ducted units.

You're definitely barking up the right tree looking for crushed ducts leaks. Your testing of ambient temp difference is spot on.

Two other things I've done in the past to try to improve performance:
1) Annual cleanings of the evaporator and condenser
2) Dropping the panels and making sure the returns and duct work are well taped (you've done this)
3) Insulating the AC covers on the outside - this may reduce the sun heat load on the compressor and other components on the roof in high-UV states like mine.

Other ideas: there is UV reflective material that you can put on the windows (clear) or consider tinting them.

I did upgrade one RV to 15k units from 13.5k, but I can't say that such made a considerable difference.

Some people have had luck moving the sensor on the evaporator fins, which can make the compressor run longer, but if you're getting 20+ degree ambient decreases at the vents, that's not your issue.


If all else fails - and I haven't had to do this on the Keystone, I have moved an AC from ducted to non-ducted in RVs where the AC unit is positioned in the right spot and that makes sense. Typically the resulting airflow is better and ambient cooling is better... This often won't work for highly partitioned trailers, but has worked for me on Class-A RVs where I didn't have a bunch of individual rooms.